The goal of this project is to explore how attentional mechanisms respond to the demands of shift-work. Previous research into human attention has largely ignored the influence of the physiological circadian rhythm and its effect on performance, while the chronopsychological literature has been concerned with atheoretical measures of performance with little reference to what cognitive psychologists have discovered about attention. Combining the two approaches will serve two purposes: (l) Gaining a better understanding of how performance changes during shift- work by relating chronopsychology to theories and findings derived from mainstream cognitive psychology; (2) Using chronopsychological methods to investigate the relationship between the attentional systems proposed in cognitive psychological theories. Subjects in a shift-work study will be tested on two important experimental paradigms from the field of selective attention: the flanker task and the visual search task. The patterns of performance in the two tasks will be correlated with each other and with physiological measures of circadian rhythm.